This study will compare binaural and monaural speech intelligibility and localization of hearing-impaired adults who will listen with and without hearing aids in the presence of varying degrees of noise and reverberation. The results of the study will identify the conditions in which the binaural advantage for intelligibility and/or localization of individual listeners can be reliably measured. Subjects will have sensorineural binaural hearing losses with various configurations of pure tone audiograms. The measurements of intelligibility will be performed for five speech-to-noise ratios, three reverberation times, monaural and binaural condition, and unaided listening (without hearing aids) and aided listening (through ear-level commercial hearing aids). The binaual and monaural localization, with and without hearing aids, will be tested with phantom sources produced by two signals arriving to the subject with a time difference. The position of the phantom source depends on the time and intensity difference of the two signals. For the aided condition, the gain controls of hearing aids will be adjusted to see if hearing-impaired subjects can achieve localization similar to that demonstrated by normal hearing subjects. A relationship between the binaural advantage for speech intelligibility and the binaural advantage for localization will be evaluated for a group and for individual subjects. This study should provide the basic data for developing a clinical test to identify those who can and cannot benefit from binaural hearing aids.